1. Field of the Invention
The present invention relates to a behavior control of a vehicle such as protecting a vehicle from spinning or drifting out, and more particularly, to a behavior control device of a vehicle adapted to estimate a saturation of the tire grip based upon a deviation of a yaw rate detected by a yaw rate sensor relative to a yaw rate calculated based upon vehicle speed and steering angle, for executing a control of the brake system of the vehicle to generate a turning moment in the vehicle acting against a spinning or a drifting out.
2. Description of the Prior Art
It is already known as described in, for example, Japanese Patent Laid-open Publication 6-115418, to execute a behavior control of a vehicle against a spinning or a drifting out by detecting that the tire grip condition is approaching a saturation based upon the above-mentioned deviation of the yaw rate. In order to accomplish such a behavior control satisfactorily, it is essential that the above-mentioned yaw rate deviation is estimated at a high precision.
However, the yaw rate sensors available to date are generally not definite in the performance thereof until they are substantially warmed up. Particularly, the presently available yaw rate sensors generally produce individually different outputs around a neutral point thereof according to each product. Such a fluctuation of the neutral point directly affects the precision of the estimation of the tire grip based upon the deviation of a yaw rate detected by the yaw rate sensor relative to a yaw rate calculated from vehicle speed and steering angle, rendering a behavior control based upon the estimation of the tire grip to be often improper in the warming up period of the yaw rate sensor.
In view of the above, it is a primary object of the present invention to provide an improved behavior control device of a vehicle having a vehicle body, a plurality of wheels suspended by the vehicle body, an engine, a steering system, and a brake system for selectively braking the wheels, the device comprising means for detecting vehicle speed, means for detecting steering angle, means for detecting yaw rate of the vehicle, and means for controlling the vehicle against a spin or a driftout according to a deviation of the yaw rate detected by the yaw rate sensor relative to a standard yaw rate estimated from the vehicle speed detected by the vehicle speed sensor and the steering angle detected by the vehicle speed sensor increasing beyond a threshold value toward a liability of the vehicle to spin or driftout, respectively, wherein any improper behavior control due to a neutral shift of the yaw rate sensor before the warming up thereof is definitely avoided.
According to the present invention, the above-mentioned primary object is accomplished by the behavior control device of the above-mentioned basic construction being improved such that the control means temporarily increases the threshold value to be higher until the yaw rate sensor is warmed up.
In the above-mentioned improvement, the warm-up of the yaw rate sensor may be judged by a predetermined time having lapsed from the start of the engine.
In the above-mentioned improvement, the control means may gradually decrease the magnitude of the increase of the threshold value according to the lapse of time from the increase thereof.
As an embodiment of the present invention, the control means may calculate an equivalent by steering angle of a neutral shift of the yaw rate sensor when the vehicle is running straight so as thereby to modify the steering angle detected by the steering angle sensor for a compensation of the neutral shift of the yaw rate sensor, and may dissolve the temporal increase of the threshold value at least for a predetermined period after an execution of the compensation even when the yaw rate sensor is not yet warmed up. In this case, the control means may calculate the equivalent by steering angle of the neutral shift of the yaw rate sensor as a mean value of each instant value thereof during a predetermined unit period. Further, the control means may modify the value of the yaw rate detected by the yaw rate sensor so as to compensate for a neutral shift of the yaw rate sensor according to an output thereof while the vehicle is stopped or running straight. Further, the control means may calculate the neutral shift of the yaw rate sensor as a mean value of an instant value thereof during a predetermined unit period.